Formula One teams return to the racetrack on Tuesday for the first tests of a new "post war" era, as well as one without Michael Schumacher.

The "tyre war" that has raged between Bridgestone and Michelin for the past six years ended with the final race of the season in Brazil last month, with the French manufacturer leaving the battleground.

For the first time since 2000, when Bridgestone was last the single supplier, the teams will all be shod by the Japanese company when testing starts up again after a five-week post-season ban.

"No amount of mathematical data can explain the subtleties of the tyres, and especially of the tyre compounds," said Pat Symonds, the Renault director of engineering whose team have won the last two championships with Michelin.

"We need to run on track in order to understand how to best use the tyres over a stint, what driving style they require, and their general strengths and weaknesses," he told the team Web site (www.renaultf1.com).

"The majority of our nine days will be spent trying to get a handle on these characteristics."

Renault, who have lost double champion Fernando Alonso to McLaren, will be testing in Barcelona with the Spaniard's replacement Heikki Kovalainen and Brazilian test driver Nelson Piquet Junior.

Italian Giancarlo Fisichella, the Finnish rookie's experienced team mate at Renault, hits the track a week later at the southern Jerez circuit.

"I don't think the move to Bridgestone can be understated, but it is also important not to overstate its importance," said Symonds. "On a technical level, the transition is one of the normal engineering challenges an F1 team faces."

FOUR BRITS

McLaren, without Alonso until January, will be in Barcelona with new signing Lewis Hamilton eager to get as much experience under his belt as possible before the season starts in Australia in March.

Kimi Raikkonen will not step into the retired Michael Schumacher's shoes at Ferrari until the New Year, with the Italian team in Barcelona with Brazilian Felipe Massa and testers Luca Badoer and Marc Gene.

Honda's Jenson Button would have joined compatriots Hamilton, Anthony Davidson and David Coulthard -- the biggest British contingent in Formula One since 2002 -- there but withdrew after cracking two ribs while karting.

Davidson will turn out for the first time as a Super Aguri race driver.

Mark Webber should slot in well enough for his first session with Red Bull, having worked with many of the personnel in the team's former existence as Jaguar.

The Australian, who is in the car on Tuesday and Wednesday before handing over to young German Michael Ammermueller on Thursday, will drive in unmarked overalls because he remains under contract to Williams until the end of the year.

Red Bull, who are switching to Renault power for 2007, will test with their existing Ferrari V8 engines.

Only three test sessions are scheduled between now and the New Year under a gentleman's agreement between the teams.